The invention relates to a device for forming a supply bobbin from a thread advanced from a yarn supply comprising a winding drum and a thread guide rotatable with respect thereto, provisions having been made to pull off this formed supply bobbin along the head of the drum.
Devices of this type form an intermediate station between the yarn supply and a yarn processing machine, such as a knitting machine, and serve to accomplish a uniform yarn pull in the direction of said yarn processing machine. The device usually operates intermittently controlled by a device detecting the yarn supply on the winding drum, e.g., in the form of a switch or a photo-electric detecting device acting on the tension of the thread windings present on the drum.
The invention aims at improving such devices for forming supply bobbins; such that predetermined thread lengths are accurately measured and delivered at accurately determined moments to the yarn processing apparatus, particularly to the weft transporting device of a shuttleless weaving machine.
This aim is achieved according to the invention by having the winding drum cooperate with a plurality of pins which are movable in an axial plane with respect to the winding drum and which are driven in a fixed transmission ratio to the movable part of the winding drum-thread guide assembly. The pins enter through a recess from a chamber within the drum into a winding space around the drum and leave said space through the recess after a displacement in the axial direction. At the moment in which a pin enters the winding space, the number of thread windings, which are present in front of that pin on the winding drum, is confined while behind it a thread bobbin determining the next thread length to be measured is built up until the next pin enters the winding space and also this second number of thread windings is completed and so on. Thereby the measured number of thread windings between two successive pins remains confined until the foremost of both pins leaves the winding space at which moment the yarn length which is lying ready may be pulled off, e.g., under the influence of the force imparted thereto by the blowing nozzle of a pneumatic weft transporting device of a weaving machine.
As compared with other yarn preparation devices as applied to shuttleless weaving machines, in which in addition to continuously rotating measuring rolls an intermittently operating yarn buffering device and a yarn clamp becoming operative at the end of the weft phase are applied, the device according to the invention offers the advantage that no special yarn clamp is necessary since the foremost of the pins confining the next series of thread windings functions as such. The series of thread windings determining the next weft may yield somewhat and thereby bring about a certain damping whereby the tension peak occurring by the stopping of the weft remains lower. This yarn stopping function, which as it were is built in the yarn preparation device is at the same time suitable for multiple application in a colour shifting system.
In the yarn preparation device according to the invention it is of course important that the pins each time accomplish a separation between the correct two successive thread windings. One may be assured thereof if in addition means are provided which bring about a uniform axial transport of the thread windings layed onto the winding drum by the thread guide. A winding drum structure may be used having radially and axially movable transport ridges according to U.S. Pat. No. 3,776,480, issued Dec. 4, 1973 in the name of John B. Lawson. With such a winding drum structure, the successive thread windings moreover are layed with an ample mutual spacing whereby the pins with certainty become operative between the correct two thread windings.
A structurally simple and preferably applied embodiment is that in which the thread guide delivers the yarn to the end face of a collar on the winding drum which gradually merges with the winding surface of the drum and in which the pins enter into the winding space at the end face of the collar. With this embodiment, the pins enter the winding space directly with their maximum radial insert height so that no provisions need be made for uniformly closing the formed thread windings. Said thread windings may simply be closed by the pins displacing in axial direction in the winding space.
According to a further feature of the invention, the pins are mounted on a disk rotatable in an axial plane within the drum chamber such that when the disk is rotated they carry out a translation movement and are always directed substantially radially with respect to the winding drum. Thereby the radial velocity or velocity component by which the pins leave the winding space is maximum which considerably decreases the dispersion in the moment in which a formed supply bobbin is released, with respect to a structure in which the pins would have a fixed radial position with respect to the disk.